This invention relates to an optical glass and, more particularly, to a high refractive and low dispersive optical glass having optical constants of 1.85 - 1.96 for Nd and 43-28 for .nu.d and consisting of a B.sub.2 O.sub.3 --La.sub.2 O.sub.3 --Gd.sub.2 O.sub.3 --WO.sub.3 --ZrO.sub.2 and/or Ta.sub.2 O.sub.5 system which is free of poisonous oxides such as ThO.sub.2, CdO and BeO and sufficiently stable to devitrification.
Various high refractive and low dispersive optical glasses containing the poisonous ingredients such as ThO.sub.2, CdO and BeO have hitherto been reported and attempts have been made to improve these optical glasses and make them harmless to humans, as disclosed in British Pat. No. 1183996, Japanese Laid-open Patent Publication Nos. 37410/1973 and 55705/1974. These improved optical glasses, however, cannot achieve a high refractivity and a low dispersion observed in the optical glasses before the improvement was made. Further, optical glasses of higher optical properties have a greater tendency to devitrification and are not suitable for mass production.